Didier wrote: >> Square root of 2 is about 1,414 or about 3,01 dB. > > I am always confused when considering noise, is it 10*log(p1/p0) or > 20*log(p1/p0)?
A moment's reflection on why the 10 log vs. 20 log, might help. The conversion from a power ratio to dB is: dB = 10 log (P1/P2) Remember that Power = VxV/R, so: P1/P2 = (V1xV1)/(V2xV2), the R's cancelling. So, dB = 10 log [(V1^2)/V2^2)] or, 10 log[(V1/V2)^2] If we want to express this as a ratio of voltages, rather than a ratio of powers (there's a pun in there somewhere ;-), we need to take the square root of (V1/V2)^2 outside of the log. To do this, we need to remember that log[X^2] = 2 log X, so: dB = 10 log[(V1/V2)^2] = 20 log[V1/V2] A couple of things to note: 1) dB's are dB's. 3dB represents the doubling of a power ratio, 6dB represents the doubling of a voltage ratio. 2) Convention says that if -dB's are loss, and +dB's are gain, but that is just convention. -Chuck Harris _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.